Is it cheaper to fly into Rio and take a bus?

Rarely. The bus from Rio to São Paulo takes 6 hours and costs about $25–$40. Unless the flight difference is more than $100, the time and effort aren't worth the small savings.

When is the most expensive time to fly?

December (due to Christmas and Summer holidays) and February (Carnival) are the most expensive. Expect to pay double or triple the normal airfare during these times.

Finding Cheap Flights to São Paulo

To get the best price for São Paulo, fly into GRU (Guarulhos) on a Tuesday or Wednesday and book exactly 3 to 4 months in advance. Use Google Flights to track prices and avoid traveling during the peak months of December and February.

Target the right airport. Search for flights into GRU (Guarulhos International). While CGH (Congonhas) is closer to the city center, it is almost exclusively for domestic flights. Unless you are connecting from another Brazilian city, GRU is where your international savings are.
Set a price alert. Use Google Flights to track the route from your home city to GRU. Toggle the 'Track prices' switch for your specific dates, and also toggle 'Any dates' if you have flexibility. You will receive an email the moment the price drops.
Fly mid-week. Avoid Friday and Sunday departures. Mid-week flights (Tuesday and Wednesday) to Brazil are consistently 15–20% cheaper because they avoid weekend business travel and leisure demand.
Check budget carriers for the final leg. If a direct flight to São Paulo is expensive, look for flights to other major hubs like Panama City (PTY), Bogota (BOG), or Miami (MIA) and then book a separate, cheaper ticket on a local carrier like LATAM or GOL to finish the journey.

Is it cheaper to fly into Rio and take a bus?: Rarely. The bus from Rio to São Paulo takes 6 hours and costs about $25–$40. Unless the flight difference is more than $100, the time and effort aren't worth the small savings.
When is the most expensive time to fly?: December (due to Christmas and Summer holidays) and February (Carnival) are the most expensive. Expect to pay double or triple the normal airfare during these times.